London: Palaeontologists and molecular biologists have been debating for decades about whether turtles are more closely related to birds and crocodiles or to lizards.

Now, two scientists from the Mount Desert Island Biological Laboratory in Bar Harbour, Maine, and their colleagues from Dartmouth College and Harvard and Yale Universities have revealed that turtles are closer kin to lizards than crocodiles.

To reach their conclusion, the research team looked at a newly discovered class of molecules called microRNA for classifying animals.

Most of the genetic material or DNA, which scientists study provides the code for building proteins, large molecules that form an essential part of every organism.

But microRNAs are much smaller molecules that can switch genes on and off and regulate protein production.

They are also remarkably similar within related animal groups and provide important clues for identification.

“Different microRNAs develop fairly rapidly in different animal species over time, but once developed, they then remain virtually unchanged,” said Kevin Peterson, a paleobiologist at MDIBL and Dartmouth College.

“They provide a kind of molecular map that allows us to trace a species’ evolution,” he stated.

Ben King, a bioinformatician at MDIBL said, “We identified 77 new microRNA families, and four of these turned out to also be expressed in the painted turtle. So we had the evidence we needed to say that turtles are a sister group to lizards and not crocodiles.”